Let's see. I worked between full and half-time when my DD was young. It was challenging since I often had to take her TO work with me. It was easier to have her at home, by far, because my lab work first involved heavy metals, and later involved biohazards and radiation. Yes, I know-- but it really (truly) was okay, and she was well-supervised and far far safer than she'd have been at preschool. (See recent thread re: food allergies in 2e).
She's always been a fairly sedentary child-- so no crawling or climbing into things, necessarily, which helped tremendously. She was also very curious, which meant that being at work with me was a lot like being in a candy store at times.
On the other hand, I also had to take her to meetings with me, and that was often interesting, particularly when she was 2-4yo and not yet reading independently. I would coach her to be SILENT during those times when I truly needed her to be invisible; I then provided her with a LeapPad (not even sure they make them now) and headphones, so that she could "read" books by herself.
I second the big magnadoodle. I had a big bag of 'tricks' that included dollar store toys when I needed something novel in a hurry, a couple of jigsaw puzzles that she could do at my desk, and a set of those magnetic building toys (DD never mouthed things-- ever-- this would't be appropriate for many 2yo, though), and some computer games like Reader Rabbit which she could play at my desktop computer while I was nearby in the lab. This left her absorbed enough that she would generally not bug other people working nearby, but it was always a bit of a tightrope act, and I thought I'd lose my mind sometimes when she was really little.
She loved to draw and read; I could leave her in a pack-n-play with a stack of board books when she was a toddler. I often did, too, so that I could grade or work up lecture notes at my desk.
